The present invention relates to the chemical vapor infiltration techniques that are used in particular when making parts out of thermostructural composite material. The invention relates more particularly to depositing matrix material in order to densify porous preforms of frustoconical shape, such as fiber preforms for use in fabricating the diverging portions of rocket engines or parts for aeroengine after-burners.
In order to fabricate parts out of composite material, in particular parts made of thermostructural composite material constituted by a refractory fiber preform (e.g. made of carbon fibers or ceramic fibers) that is densified by a refractory matrix (e.g. made of carbon and/or ceramic), it is common practice to make use of chemical vapor infiltration methods. Examples of such parts are thruster nozzles made of carbon-carbon (C—C) composite material, brake disks, in particular for airplane brakes, made of C—C composite materials, and ceramic matrix composite (CMC) turbine blades.
Densifying porous preforms by chemical vapor infiltration consists in placing the substrates in a reaction chamber of an infiltration installation by means of support tooling, and in admitting a reagent gas into the chamber, which gas has one or more components that are precursors for the material that is to be deposited within the preforms in order to densify them. Infiltration conditions, in particular the composition and the flow rate of the reagent gas, and also the temperature and the pressure inside the chamber, are selected so as to enable the gas to diffuse within the accessible internal pores of the preforms so that the desired material is deposited therein by a component of the gas decomposing or by reaction between a plurality of components of the gas. The reagent gas is usually preheated by being passed through a preheater zone situated in the reaction chamber and into which the reagent gas inlet leads. That method corresponds to the free flow chemical vapor infiltration method.
In an industrial installation for chemical vapor infiltration, it is common practice to load the reaction chamber with a plurality of preforms to be densified simultaneously in order to increase the throughput of the densification process, and consequently to increase the specific loading of reaction chambers.
Methods and installations for densifying porous annular substrates by chemical vapor infiltration are described in particular in U.S. Pat. No. 7,182,980 and U.S. Pat. No. 5,904,957. Nevertheless, those methods rely essentially on densifying substrates of annular shape arranged in stacks and, in terms of optimizing loading, they are not suitable for densifying preforms of frustoconical shape and of large dimensions. As described in U.S. Pat. No. 7,182,980 and U.S. Pat. No. 5,904,957, it is necessary to leave a large amount of space between each frustoconical preform in the reaction chamber so as to enable the infiltration gas to feed every portion of the preforms for densifying in a manner that is satisfactory, thereby significantly reducing the loading capacity of each infiltration installation and increasing the cost of fabricating parts. Producing parts that are frustoconical in shape and of large dimensions on an industrial scale thus requires a large number of infiltration installations to be built and used, which is highly penalizing in economic terms.